An economic approach to animal models of alcoholism.

Researchers have long sought an animal model for human alcohol consumption. This article describes an economic-based approach to a model of alcohol preference in rats. The procedures are based on an analogy between clinical accounts of human drinking and the economic analysis of consumption. Both clinical and economic investigators typically define consumption patterns in terms of the influence of negative consequences. For example, the clinical account emphasizes the persistence of heavy drinking despite mounting alcohol-related aversive consequences, and in economic analyses, the term "inelastic demand" is used to refer to the persistence of consumption despite large increases in prices. In the experimental procedure described here, rats worked for alcohol and food. Presses on one lever earned a drink of 10 percent alcohol plus saccharin, and presses on a second lever earned isocaloric drinks of a starch solution. After behavior stabilized, the response requirements (which are analogous to prices) for one or both drinks were increased. The rats maintained baseline alcohol consumption levels despite large increases in the "price" of alcohol. In contrast, the same price increases markedly reduced starch intake. That is, food consumption was sensitive to price hikes, but alcohol consumption was not. The results demonstrate that a common economic framework can be used to describe human and animal behavior and, hence, the possibility of an animal model of human alcohol consumption. The article also points out that economic concepts provide a framework for understanding a wide range of human drinking patterns, including controlled social drinking and excessive alcoholic drinking.

F or more than half a century, re s e a rchers have been plying rats with alcohol in the hope of deve loping a valid animal model of human alcohol consumption (e.g., Richter and Campbell 1940). Fo l l owing up on the o b s e rvation that alcoholism tends to run in families, one strategy has been to breed alcohol-consuming rats (e.g., Li and Lumeng 1984). Other re s e a rc h facilities have focused on drinking hist o ry. For example, Samson and his colleagues (1988) found that rats that drank sweetened alcoholic drinks would subsequently drink larger amounts of unsweetened alcohol solutions. Our approach has been to manipulate the economic conditions gove r n i n g access to an alcoholic drink. The rats we re placed in a setting in which leve r p resses would earn either a swe e t e n e d alcohol drink or food. We then va r i e d the number of times the rats had to p ress the levers in order to obtain alcohol, food, or both. In this way, it was possible to examine the re l a t i o n s h i p b e t ween the "price," defined as the leve r p ress re q u i rement, and alcohol consumpt i o n . For example, would an increase in price have more of an effect on alcohol consumption or on food consumption? The theoretical background for this a p p roach includes clinical accounts of drinking, such as those provided by the American Ps ychiatric Association ( A PA) (1994), and elementary economic ideas concerning the re l a t i o nship between changes in price and changes in consumption. This art i c l e begins with the clinical account of alcohol consumption, as it sets the stage for this and all animal models of human drinking.

Clinical Account of Drinking and the Economic Account of Consumption: An Analogy
The APA publishes a widely used diagnostic manual (i.e., the Diagnostic and Statistical Manual of Mental Disord e r s or DSM [1994]) that includes a set of criteria for identifying individuals as "a b u s e r s" of alcohol or as "d e p e n d e n t" on alcohol. The diagnoses are based on e x p e rt opinion and field re s e a rch, and for many syndromes, including pro blem drinking, they yield a substantial d e g ree of inter-rater reliability (e.g., Sp i t zer et al. 1978). For instance, there is more than an 80-percent likelihood that different clinicians will agre e whether a part i c u l a r individual meets or does not meet the criteria for "a l c ohol dependence" (e.g., He l zer et al. 1977;Robins et al. 1982). Thus, the m a n u a l's account of human drinking p roblems provides a reasonable target for animal pro c e d u re s . Ac c o rding to the most recent edition of the DSM (APA 1994), pro b l e m drinking is defined primarily by the d e g ree to which drinking persists in the face of alcohol-related ave r s i ve eve n t s . Those who abuse alcohol or are dependent on alcohol repeatedly get dru n k despite previous drinking-related pro blems, such as arrests, fights, and poor job performance (p. 196). In addition, the alcohol dependent drinker, who is c o n s i d e red to have a more serious pro bl e m , d e velops tolerance to alcohol's i n t oxicating effects, suffers withdrawal symptoms and, when attempting to quit drinking, relapses back to heavy alcohol use. (In other words, "a l c o h o l d e p e n d e n c e" approximates the more commonly used term "a l c o h o l i s m . " ) The influence of alcohol's negative consequences is also used to identify social or nonproblem drinkers. The DSM states it this way (p. 194): as many as 90% of adults in the United States had some experience with alcohol, and a substantial number (60% of males and 30% of females) have had one or more alcohol-re l a t e d a d verse events (e.g., driving after consuming too much alcohol, missing school or work due to a hangover). Fo rt u n a t e l y, most individuals learn from these experiences to moderate their drinking and do not develop Alcohol Dependence or Ab u s e .
Thus, the influence of drinkingrelated problems on future drinking is the criterion for differentiating healthy and unhealthy drinking patterns, with the healthy taking due heed.
Although the purpose of the DSM account is to help clinicians and res e a rchers differentiate problem and nonp roblem drinkers, the logic of the a p p roach follows closely the logic of the economic analysis of consumption. The key terms in the economic approach are changes in price and changes in the leve l of consumption. For many goods, a change in price has a profound effect on consumption. For example, studies show that when the price of green peas or restaurant meals increases, consumption of these commodities decreases, and the re l a t i ve size of the change in consumption is considerably larger than the re l a t i ve size of the change in price (Houthakker and Taylor 1970;Frank 1991). The technical term for these examples is "e l a s t i c demand," with "e l a s t i c" referring to the fact that consumption ranges widely in response to re l a t i vely small increments or d e c rements in price.
Howe ve r, consumption is not a l w a y s s e n s i t i ve to changes in price. For e x a m p l e , when the price of health care or gasoline goes up by say 100 percent, the decre a s e s in consumption are typically less than 50 p e rcent (e.g., Nicholson 1985). As a re s u l t , the consumer spends m o re on the goods but gets less. The technical term for this situation is "inelastic demand." Although the terms ("e l a s t i c" and "inelastic") suggest a continuum, there is a qualitative difference. Instances of "inelastic demand" are at best unpleasant and when persistent or extreme inspire action to "c o r re c t" the markets, as in the call for gove r nment regulation of health costs or the recent blockade of fuel depots by Fre n c h t ruck drivers protesting soaring gasoline prices. This is re l e vant because there is a connection between inelastic demand and problem drinking.

Inelastic Demand for Alcohol as a Component of Problem Drinking
The logic of elasticity of demand parallels the logic of the DSM's description of drinking patterns. Both accounts focus on the relationship between behavioral c o n s equences and the future likelihood of the behavior. When the DSM authors state that a social drinker is someone who is influenced by the ave r s i ve consequences of alcohol, they are in effect saying that for social drinkers, demand for alcohol is re l at i vely elastic. For instance, by definition, social drinking occurs under socially a p p roved conditions, and it ceases to be social drinking if consumption re p e a tedly leads to extreme intoxication or debilitating hangovers. Si m i l a r l y, to say that those who are alcohol abusers or alcohol dependent continue to drink heavily despite past alcohol-dependent ave r s i ve consequences is to say that alcohol consumption is inelastic. It persists, despite i n c reased and mounting costs. The analogy does not, of course, cover all of human drinking. For instance, it treats the drinker (and the rat) as a "black box , " omitting the biological and psyc h o l o g i c a l c o r relates of drinking. Howe ve r, this is the p roper starting point for an animal model. That is, before exploring the biology and psychology of rat drinking, t h e re should first be some basis for expecting that the mediating mechanisms will be re l e vant to the human case. be re m oved, so the experimenter must s o m e h ow minimize or neutralize t h e i r influence to establish that alcohol's pharmacological effects are influencing b e h a v i o r. To reduce the influence of calories, we arranged a concurrent highly palatable food that provided the same number of calories as the alcohol. Fo r instance, in all of the studies discussed in this re p o rt, the rats had access to solutions of starch or sucrose as well as alcohol. The point was to see if changes in the experimental conditions bro u g h t about similar or different changes in alcohol and food consumption. If the consumption patterns proved similar, then the underlying motivational basis must be similar. If the consumption patterns proved to be different, then it is reasonable to infer that the mechanisms governing consumption differe d . For example, increases in body we i g h t d e c rease food consumption. Wo u l d they also decrease alcohol consumption? A l t e r n a t i ve l y, "f re e" alcohol decre a s e s a l c o h o l -m o t i vated behavior. Would it also decrease food-motivated behavior?
To reduce the influence of alcohol's a ve r s i ve taste and to make alcohol taste m o re like the control solutions, we mixe d it with saccharin. As most re s e a rc h e r s w o rking with animal models prov i d e their subjects alcohol mixed with water, this aspect of the pro c e d u re deserve s some additional background.
Alcohol mixed with water stimulates both "s we e t" and "bitter" re a c t i o n s (Kiefer et al. 1990), and as concentration increases, the bitter reaction dominates (e.g., Richter and Campbell 1940). Howe ve r, despite these facts, the tradition is to present rats alcohol mixe d with water. The following facts persuaded us that palatability was the better course.
The addition of saccharin more than doubled alcohol intake, pro d u c i n g blood alcohol levels that we re two to four times greater than obtained with s e l e c t i vely bred, alcohol preferring (P) rats under otherwise similar circ u mstance (compare Heyman et al. 1996 with Schwarz -St e vens et al. 1991). As pharmacological influence on cons u m p t i o n is a function of blood alcohol l e vels, this difference means that the saccharin pro c e d u re is more likely to lead to pharmacologically based pre f e r-ences. In support of this point, it has not proved possible to motivate rats to w o rk for alcohol mixed with water when t h e re is a palatable food like sugar ava i lable. Mo re ove r, this is the case even for s e l e c t i vely bred, alcohol preferring (or P) rats (e.g., Schwarz -St e vens et al. 1991). In contrast, commercially bred as we l l as selectively bred alcohol-pre f e r r i n g (P) and alcohol-nonpreferring (NP) rats readily drink large amounts of alcohol plus saccharin in the presence of palatable and pre f e r red foods (e.g., He y m a n 2000). These findings provide the re s e a rcher with a critical methodological a d vantage. If the rats continue to drink alcohol and saccharin mixtures when they also have access to palatable foods, then it is possible to introduce contro l solutions that provide the same caloric density as alcohol. Thus, we we re able to test if alcohol consumption was motiva t e d by calories or by its pharmacology.
A coro l l a ry of this discussion is that the re s e a rcher does not re m ove the influence of taste by mixing alcohol with w a t e r. Rather, the re s e a rcher has the option of providing his or her subjects with a more or less ave r s i ve -t a s t i n g a l c ohol solution. The evidence to date supp o rts the more palatable approach.

The Experiments: Response Requirement as Price
We conducted a series of experiments in which the price of sweetened alcohol drinks and the price of sucrose and s t a rch solutions we re varied. In some studies, the price of each substance was changed one at a time. In others, the price of each commodity was changed in tandem. The "t a n d e m" study will be g i ven the most attention as it re ve a l s the behavioral processes most clearly.
The experimental chamber held two l e vers and two dippers. At one lever the rats could earn a drink of 10 perc e n t alcohol plus saccharin. At the other leve r the rats could earn a drink of starc h solution (i.e., Po l ycose), with the concentration set to provide the same numb e r of calories per milliliter (mL) as the alcohol ("isocaloric solutions"). Pr i c e was re p resented by the response re q u i re-ment for earning a drink. In the initial condition of the study, the re q u i re m e n t was 5 responses for both the alcohol solution and the starch solution. Fo r instance, in a 45-minute session, there we re about 600 alcohol lever pre s s e s and about 1,200 starch lever presses so that the rats earned approximately 12 mL of 10 percent alcohol solution and 24 mL of starch solution. This is a ve ry high rate of intake. For instance, it is e q u i valent (by weight) to a 165-pound person drinking about 6.4 ounces of p u re alcohol, or two six packs of domest i c b e e r, in 45 minutes. (Each mL of alcohol provides about 0.79 grams of alcohol, there are about 28.6 grams to an ounce, the rats weighed about 390 grams, and the alcohol content of beer varies between about 4 and 5 perc e n t . ) In subsequent conditions, the prices we re increased in 50 or 100 perc e n t steps, leading to a final set of prices of 30 lever presses for each drink. Each price was in effect until consumption l e vels stabilize d .

Price and Income
The nominal experimental manipulation was a change in response re q u i rements. If this is seen as a change in price then there is the additional implication of a change in real income. Fo r instance, under ord i n a ry circ u m s t a n c e s i n c reases in prices and a reduction in the monthly paycheck are equivalent in that both reduce purchasing powe r. But what is the equivalent of "income" for rats that earn their keep by pre s s i n g l e vers? The closest analogy is the number of possible alcohol and food drinks. For instance, since the session length was fixed at 45 minutes, increases in the response re q u i rements inva r i a b l y d e c reased the total number of possible s t a rch and alcohol servings. Thus, changes in consumption patterns may reflect changes in the overall ava i l a b i l i t y of alcohol and food as well as changes in price. (Note that price and commodity availability [income] are logically distinct. For example, we could h a ve increased price and kept the ove rall availability of food and alcohol constant by increasing session length in p ro p o rtion to the price incre a s e s . )

Changes in Price Had Less Influence on Alcohol Consumption
The relationship between increases in the response re q u i rements and changes in alcohol and food consumption is s h own in figure 1 below. The axes are logarithmic because in econometric studies this transformation often yields a linear relationship between the va r iables. As was expected, price incre a s e s d e c reased food consumption. Each doub l i n g of the price reduced starch consumption by about 40 percent of its c u r rent value. The relationship was linear (in logarithmic coordinates), meaning that re l a t i ve increases in price had about the same re l a t i ve effect on food consumption over the entire range of prices. Also note that the re l a t i ve decre a s e in food intake was somewhat less than the re l a t i ve increase in price so that demand for food was somewhat inelastic. (The slope was less than -1.0.) Price increases had a quite differe n t effect on alcohol consumption. For the first four price hikes, alcohol consumption either increased or stayed about the same. Indeed, it was not until the response re q u i rement had increased by 500 percent re l a t i ve to baseline, 30 responses per drink, that alcohol intake declined. As alcohol consumption both i n c reased and decreased, a straight line does not describe the results. Howe ve r, for purposes of comparison, a line was fit to the data points. The slope did not differ significantly from 0.0. In other w o rds, increases in price did not systema t i c a l l y d e c rease alcohol consumption, which is to say that demand for the alcohol solution was highly inelastic. This implies that there must have been m a rked increases in responding at the alcohol lever (see figure 2).
Fi g u re 2 shows lever pressing for alcoh o l and for food. Again the re s p o n s e re q u i rement (i.e., "p r i c e") is plotted on the x-axis, but now the pro p o rtion of responses allocated to the lever that opera t e d the alcohol dipper is plotted on the y-axis. When each substance cost just five responses, the alcohol lever was chosen about 33 percent of the time. Howe ve r, as price increased, responding shifted to alcohol, so that the overall re s p o n s e allocation ended up in favor of the alcohol solution. Thus, there was a powe rf u l c o r relation between increases in price, decreases in income, and incre a s e s in alcohol seeking.
These results are re p re s e n t a t i ve of a series of experiments in which prices and income we re varied (e.g., Pe t ry and Heyman 1995). In each study, manipulations that produced substantial d e c reases in food consumption had little influence on alcohol consumption. That is, demand for alcohol was always g reater than was demand for food, and in each study, pre f e rence shifted fro m food to alcohol as prices increased or income decreased. Im p o rt a n t l y, the results did not have to work out this w a y. Alcohol consumption could have d e c reased as much or more than did food intake. For example, in a similar experiment in which lever presses pro-duced different types of food (i.e., sugar and starch), increases in price re s u l t e d in roughly pro p o rtionate decreases in the consumption of both foods (He y m a n et al. 1999). As a result, pre f e re n c e remained unchanged over a wide range of price and income leve l s .
That changes in alcohol and food consumption we re uncorrelated ove r most price increases suggest the factors c o n t rolling consumption of each differe d in one or more important ways. In the language of economics, the results suggest starch was not a "s u b s t i t u t e" for the s weetened alcohol drink and vice ve r s a , e ven though both substances we re consumed in the same way. This observation can be tested by separately incre a sing the price of each substance. If they a re substitutes, then consumption will shift to the one with the cheaper price.

Vol. 24, No. 2, 2000 135
An Economic Approach to Animal Models Figure 1 Increases in alcohol "price" decreased the amount of starch that rats consumed but failed to decrease their alcohol consumption except at the highest alcohol price level (i.e., 30 responses). The data are graphed in logarithmic coordinates to show that a linear plot occurred when relative change in consumption was proportional to relative price increase. This finding, however, was true for starch consumption but not for alcohol consumption. As indicated by the data points, approximately seven rats dominated the last three sessions of each condition.
For example, econometric studies show that increases in the price of butter lead to an increase in margarine consumption and vice versa (e.g., Frank 1991). Thus, we arranged conditions so that the behavioral re q u i rements for each substance increased one at a time. As suggested by the results shown in figure  1, increasing the price of alcohol did not result in increased consumption or p re f e rence for food, and conve r s e l y, i n c reasing the price of food did not re s u l t in increased consumption or pre f e re n c e for alcohol. This is a surprising re s u l t g i ven that both substances are ingested and provide calories. Howe ve r, for humans, it is also the case that there a re settings under which nonalcoholic drinks are poor substitutes for alcoholic ones. When a social drinker is at a bar or cocktail part y, soft drinks are usually a distant second to wine and beer.

Alcohol Regulated Preference: The Conservation Hypothesis
From the perspective that price incre a s e s a re ave r s i ve, it is counter-intuitive that a l c o h o l -re i n f o rced responding incre a s e d . Howe ve r, there is a principle that explains this apparent discre p a n c y. If the rats we re m o t i vated to maintain baseline levels of alcohol (but not starch), the results are quite sensible. Notice that the contingencies we re stru c t u red so that it was possible to keep alcohol consumption l e vels constant if responding incre a s e d in direct pro p o rtion to the re s p o n s e re q u i rement increments. Up to a thre efold hike in response costs, this is exactly what happened at the alcohol leve r. In other words, the quantitative feature s of the changes in behavior could be deduced from the assumption that the r a t s' strongest motivation was to maintain a constant daily ration of alcohol.
If the conservation hypothesis is c o r rect, then it should also be possible to arrange conditions that induce the rats to decrease their pre f e rence for alcohol. This was tested in a study that p rovided "f re e" servings of alcohol ( Heyman 1993). As in the experiment associated with figures 1 and 2, leve r p resses earned either a sweetened alcohol drink or food. Howe ve r, the chamber also held a dish filled with va ry i n g amounts of sweetened alcohol. The rats would first drink from the dish and then, after the dish was empty, start leve r p ressing for alcohol and food. The basic finding was that alcohol-re i n f o rc e d responding declined, and the magnitude of the decrease was pro p o rtional to the amount of alcohol that was in the dish. Mo re ove r, the total amount of alcohol consumed remained approximately cons t a n t at about 1.25 to 1.5 mL per session (which is about the same as the amounts earned in the experiment summarize d by figures 1 and 2). In contrast, fre e alcohol did not lead to decreases in food consumption. These findings demonstrate that lever pressing was in the service of alcohol, decreasing or i n c reasing as dictated by the experimental manipulations and the alcohol c o n s e rvation principle.
The immediate goal of these experiments was to establish a model of human drinking. The criteria we re (1) d i f f e rent patterns of food and alcohol consumption, (2) the persistence of alcohol consumption despite the ava i lability of highly pre f e r red competing activities, and (3) that increases in the cost of responding should have less of an effect on alcohol than on other n o rmally effective re i n f o rcers. It seems fair t o say that these goals we re met. In addition, in experiments like the ones just described, the rats developed t o l e r a n c e to alcohol's intoxicating effects as meas u red by tasks such as the ability to walk on a rod and to regain an upw a rd post u re when dropped b a c k w a rds from a s h o rt height onto a p i l l ow (Shegog 1991).

Why Did In c reases in Price De c re a s e Food But Not Alcohol Co n s u m p t i o n ?
Although the solutions we re isocaloric, it is possible that alcohol's food-re l a t e d Figure 2 Preference for the alcohol solution as a function of "price" change among study rats. The x-axis displays the response requirement and the y-axis displays the proportion of responses at the alcohol lever. The data points show the average response of seven rats during the final three sessions of each condition.

An Economic Approach to Animal Models
effects, such as its taste, motivated the rats. This line of inquiry is not likely to shed much light on alcohol abuse or dependence, but the issue needs to be a d d ressed before pursuing ideas more likely to be re l e vant to human drinking. The experiments we re based on the assumption that if demand for alcohol was based on taste, then it should be possible to show that taste is a sufficient c o ndition for establishing inelastic demand.
In the first taste test, the two competing re i n f o rcers we re a sucrose solution and a sucrose plus bitter quinine solution (Heyman 1997). In i t i a l l y, prices we re the same for both solutions, and then each was increased in turn. If taste establishes a basis for inelastic demand, the rats should resist the l ower price and stick with their initial, taste-based pre f e rences. At first, the rats p re f e r red the sucrose solution without quinine by a margin of about four to one. Howe ve r, when the price of the quinine solution became re l a t i ve l y ch e a p e r, the rats readily switched to it, despite their initial aversion. Conve r s e l y, when the price of the plain sucro s e solution decreased, the rats re a d i l y i n c reased their pre f e rence for it. Un l i k e the alcohol studies, there was no sign of inelastic demand. A study with two d i f f e rent foods, starch and sucro s e ( Heyman et al. 1999), showed the same pattern of results. Thus, flavo r and macronutrient content did not establish the conditions for inelastic demand. This suggests that flavor and related factors do not explain inelastic demand in the alcohol studies.

Pharmacologically Induced Selective Changes in Alcohol Consumption
Because alcohol consumption and food consumption are clearly distinguishable in the concurrent choice experiments just re v i ewed, the pro c e d u re provides a strategic baseline for identifying the biol o g i c a l mechanisms that mediate alcohol consumption. One study showe d that Ro15-4513, a drug that acts at the same receptor (i.e., the docking) site on the cell membrane as the benzo d i a ze p i n e t r a n q u i l i zers Va l i u m ® and Librium ® , p roduced small but significant decre a s e s in alcohol consumption at doses that did not decrease sucrose consumption ( Pe t ry 1995). Fi g u re 3 below shows that d a i d z i n , a naturally occurring isoflavo n e , p roduced greater changes. At each dose it reduced alcohol consumption, and the decreases in alcohol intake we re always larger than the decreases in food intake (Heyman et al. 1996). Also, in this experiment blood alcohol was meas u re d . The range was 50 to 304 mg/dl, and the a verage was 139 mg/dl. In other rat self-administration studies, blood alcohol levels are usually not gre a t e r than about 80 mg/dl (e.g., Schwarz -St e vens et al. 1991), and the criterion for dru n k d r i ving is usually between 80 and 100 mg/dl.
The results from this last study are of special interest because daidzin is a constituent of a traditional Chinese tre a tm e n t for problem drinking. Chinese herbalists use the root of the kudzu plant to treat drinking problems (Keung and Vallee 1998b). Daidzin is derived fro m this root, and recently Dr. Keung and Dr. Vallee of Ha rva rd Medical School found a correlation between daidzin's ability to inhibit alcohol drinking in rodents and its ability to inhibit sero t o n i n and dopamine metabolism in isolated l i ver mitochondria (Keung and Va l l e e 1 9 9 8a). Thus, anecdotal re p o rts of human behavior and in vitro laboratory findings are consistent with the animal model data. Howe ve r, direct tests of d a i d z i n's influence on human alcohol consumption have yet to be undert a k e n . food consumption among study rats. The decreases in alcohol intake, however, were greater than the decreases in food consumption, and these differences increased in relation to dose. The data points show an average of seven rats. Each daidzin dose was administered three times, saline was administered five times, and baseline was defined as the session just preceding the saline session.
*Daidzin is derived from a plant used by traditional Chinese herbalists to treat excessive drinking (Heyman et al. 1996).

Implications: Does Economics Apply to Human Drinking?
El e m e n t a ry economic ideas provided the conceptual framew o rk for the experimental pro c e d u res described in this art i c l e . Might economics also provide a framew o rk for understanding alcoholism? Ac c o rding to the DSM, addiction, including alcoholism, is "c o m p u l s i ve" d rug consumption. Ac c o rding to the d i c t i o n a ry (e.g., American He r i t a g e 1992), a compulsion is an irre s i s t i b l e act that is either irrational or occurs re g a rdless of its rationality. Howe ve r, an implication of the analogy betwe e n inelastic demand and problem drinking is that alcohol dependence and alcohol abuse reflect pre f e rences for alcohol not i r resistible urges. For instance, inelastic demand is a function of the economic conditions, in particular the absence of substitutable goods or activities. Thus, if this viewpoint applies, it should be possible to arrange conditions that bring drinking in alcoholics to a halt. Se veral lines of evidence support this i n f e rence.
A series of experiments conducted in the 1970s showed that price incre a s e s would curb drinking in alcoholics (e.g., Bi g e l ow and Liebson 1972; Cohen et al. 1971b). In one of the more re a l i s t i c studies, alcoholics we re given a priming dose of alcohol and a monetary rew a rd if they drank no more than the initial drink (Cohen et al. 1971a). The subjects opted for the monetary rew a rd, but as the concentration of the initial priming dose increased, the size of the monetary rew a rd re q u i red for abstinence incre a s e d . That is, the alcoholics had a price, and the price depended on the pharmacological impact of the drink. Also note that the alcoholics we re more sensitive to price increases than the rats in the l a b o r a t o ry studies. Ac c o rding to economic theory this means that in the human study there we re more activities that could substitute for drinking than in the rat study. This seems a re a s o nable explanation, as the rats lived in an e n v i ronment where there we re only a f ew obvious re i n f o rcing activities: eating chow, eating starch, drinking alcohol, and drinking water.
The human studies we re conducted in isolated residential settings, and it is legitimate to point out that although these settings may have been richer than those in the rat studies, they we re art i f icial. Howe ve r, such criticisms miss the point that cost-benefit contingencies curbed drinking in alcoholics-eve n when the alcohol was accessible and eve n when some drinking had already occurre d . On the basis of data such as these, Vuchinich and Tucker (1988) demonstrated that choice theory can describe alcoholic drinking patterns, and in a series of papers on relapse and abstinence, they extended the 1970s laborat o ry findings to natural settings (e.g., Tucker et al. 1995).
If economics and choice theory describe alcoholic drinking patterns, then social drinking and alcoholism differ in degree rather than kind. Fo r example, both social and alcoholic drinking can be described in terms of the number of situations in which demand for alcohol is inelastic. Fo r social drinkers, demand is somew h a t inelastic in settings such as bars and cocktail parties, but not at home in the early morning or afternoon. In c o ntrast, for many alcoholics, demand f o r alcohol is inelastic at bars and at home in the early morning. Put another way, social drinkers inhabit more settings in which alcohol has a substitute.
Fi n a l l y, it should be pointed out that the economic analysis does not deny the i m p o rtance of biological influences on drinking or the potential value of an e f f e c t i ve pharmacological treatment for alcoholism. For instance, economic a p p roaches to addiction imply that t reatment should include practices that s t rengthen behaviors that will substitute for the drug (e.g., Higgins et al. 1994). This approach would be greatly facilitated by pharmacological agents that attenuated or blocked the immediate p o s i t i ve effects of the drug. This would i n d i rectly increase the value of competing activities, and periods of sobriety would give such activities time to take root. Thus, economics provides principles for developing effective animal models of human drinking and a f r a m ew o rk for fitting together the many biological and experiential factors that influence human drinking, including alcoholism. s

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